Get projection/crs from GMT_GRID_HEADER

### Description of the desired feature

This is a feature request to add a method for getting the projected coordinate reference system (CRS) from a GMT_GRID (#2398)/GMT_IMAGE (#3338)/GMT_CUBE (#3150) struct when parsing a NetCDF/GeoTIFF file. Motivation from https://github.com/GenericMappingTools/pygmt/pull/2235#discussion_r1780317848:

>> In `GMT_IMAGE.to_dataarray()`, perhaps we should parse the `header->ProjRefPROJ4` and set the correct CRS to the 3-band xarray.DataArray. ...
>
> Yeah, I was thinking of parsing the projection information from the header when you mentioned this `ProjRefPROJ4` field at https://github.com/GenericMappingTools/pygmt/pull/3128#discussion_r1779965090. But ideally we'll need to handle PROJ4/WKT/EPSG:
>
> https://github.com/GenericMappingTools/pygmt/blob/f97c3a462a0d65e10da7707a71c9cc991457759a/pygmt/datatypes/header.py#L138-L143
> ...

### Implementation details

Use [`pyproj.CRS.from_string`](https://pyproj4.github.io/pyproj/stable/api/crs/crs.html#pyproj.crs.CRS.from_string) to make a CRS from PROJ4/WKT/EPSG. Create a new method/property under `_GMT_GRID_HEADER` at https://github.com/GenericMappingTools/pygmt/blob/v0.13.0/pygmt/datatypes/header.py#L67

We can also consider exposing a `.gmt.proj` or `.gmt.crs` xarray accessor property (xref #499). But note that there is some discussion at https://github.com/geoxarray/geoxarray/issues/21 on whether there should be a common `.crs` accessor in some xarray library that can be used across [rioxarray](https://github.com/corteva/rioxarray)/[geoxarray](https://github.com/geoxarray/geoxarray)/[odc-geo](https://github.com/opendatacube/odc-geo)/etc.

### Are you willing to help implement and maintain this feature?

Yes